Semiconductor integrated circuit for brushless motor drive control and brushless motor drive control apparatus

ABSTRACT

A pulse current having such a short duration as the rotor does not react is passed through field coils of respective phases of a brushless motor in first and second, mutually opposite, directions sequentially, voltages induced, by the pulse currents in two directions at each of the field coils of the non-conducting phase are combined, the polarity of a combined voltage is detected, and a field coil pair where a current is to be passed to start the motor is determined based on the result of detection for each of field coil of the non-conducting phase.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a technique for drive control ofa brushless motor and a technique effective when applied to a method fordetermining phases (a pair of phases) at which to start currentconduction when starting the motor, and particularly concerns atechnique effective when used in a drive control apparatus of a spindlemotor for rotating a disk-type storage medium, such as a HDD (hard diskdrive) device.

[0002] With hard disk devices, there has been a strong demand for higherspeed in writing and reading information on a magnetic disk, namely,quicker access speed. To this end, it is required that the spindle motorbe made much faster. In addition, demand is also mounting for reductionsin size, power consumption and production cost of the drive controlapparatuses. In conventional hard disk devices, DC polyphase brushlessmotors are generally used for their spindle motor to rotate the magneticdisks at high speed, and information is written or read on the rotatingmagnetic disk by bringing the read/write magnetic heads into contactwith or in close vicinity to the disk.

[0003] In brushlress motors, there has been used a motor drive controlmethod by which to prevent reverse rotation of the motor by detectingthe positional relation of the rotor and the stator by means of Hallelements and by, from the detected positional relation, determiningfield-coil phases at which current conduction is to be started. Becausemounting a rotor position detector using Hall elements in the motorincreases the difficulty of downsizing the motor, sensorless motors havecome to be used in large numbers in the hard disk devices. However, ifthe magnetic disk is driven by a sensorless motor, the rotor is likelyto make a reverse rotation for an instant with a probability of ½ whenthe disk starts to rotate.

[0004] With the rapidly multiplying storage density of the magneticdisks in hard disk devices in recent years, the magnetic read/writeheads have been sharply reduced in size. Consequently, in the hard diskdevices with the magnetic heads miniaturized to such an extent, there isa problem that if the rotor is turned in reverse even for an instant,the magnetic heads may suffer a fatal damage. To solve this problem, acontrol method has been proposed in which a pulse current of so short aduration as not to cause the rotor to react is supplied to the fieldcoils of the stator, and the field coils where the amplitude is at themaximum value, in other words, the phases, where the field of the rotormagnet in the same direction as the generated field of the coils,causing magnetization to be saturated to make current flow most easily,are determined as the phases at which to start current conduction (Referto JP-A-63-694895 published on Mar. 29, 1988 which corresponds to U.S.Ser. No. 880,754 filed on Jul. 1, 1986).

[0005] Another control method has been proposed in which a pulse currentis conducted through the field coils of the stator and then the pulsecurrent is conducted in the opposite direction, and differences incurrent rise time constant are detected at respective field coils wherethe current is passed through, and according to detection results, theposition of the rotor is determined to determine a pair of phases atwhich current conduction is started. In other words, this control methodis such that phases at which current conduction is started aredetermined by determining the rotor position based on detection resultsobtained by detection of differences in inductance by making use of aphenomenon that the inductance of the field coils varies whether thedirection of the magnetic field is the same or not between the fieldcoils and the rotor magnet (that is to say, whether magnetic saturationoccurs or not) (Refer to JP-A-3-207250 published on Sep. 10, 1991 whichcorresponds to U.S. Ser. No. 413,311 filed on Sep. 27, 1989).

[0006] In addition to the above inventions, another invention has beenproposed that the stopped position of the rotor is determined byapplying a diagnosis signal of a frequency higher than the frequency ofan exciting signal applied when the motor is started, to a single coilor two or more coils connected in series and detecting an inducedvoltage of one of the serially-connected coils (Refer to JP-A-7-274585published on Oct. 20, 1995).

SUMMARY OF THE INVENTION

[0007] However, the present inventors have revealed that the prior artdescribed above suffer problems as follows.

[0008] In the control method that determines a pair of phases, wherecurrent conduction is started, by passing a pulse current and detectingthe maximum amplitude value, the maximum amplitude value depends onvariations in winding in the field coils of the stator, for which reasondetection errors occur due to very small winding variations that areunavoidable in the manufacturing process. In the control method thatdetermines a pair of phases, where current conduction is started, bydetecting the rotor position based on differences in current rise timeconstant, because a phenomenon of magnetic saturation is used,differences in time constant do not become conspicuous unless a fairlylarge current is passed, and therefore it is difficult to detectdifferences in the time constant when a current passed is so small asthe rotor does not react to it. Another problem with this control methodis that the point of reversal of the large-small relation among the timeconstants that occurs when the direction of a current is reversed doesnot coincide with the point of magnetic saturation, resulting in errorsin determination results.

[0009] The present invention has as its object to provide a brushlessmotor drive control technique that can prevents reverse rotation of themotor at starting by detecting the position of the rotor relative to thestator with fewer errors and determining a field coil pair at whichcurrent conduction is started.

[0010] According to an aspect of the present invention, a pair of phasesfor current conduction to start the motor is determined by passing apulse current with a duration so short as the rotor does not reactthrough the field coil of any phase of the motor in first and second,mutually opposite, directions sequentially, and detecting inducedvoltages in the non-conducting phase by a pulse current in two oppositedirections, combining voltages induced by a pulse current in the firstdirection and a pulse current in the second direction, detecting thepolarities of combination results, and determining a pair of phases forcurrent conduction when starting the motor based on polarity detectionresults related to a plurality of the conducting phases.

[0011] The above-mentioned and other objects and features of the presentinvention will become obvious from the following description of thisspecification and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIGS. 1a and 1 b are schematic diagrams illustrating the principleof a rotor position detecting method according to one embodiment of thepresent invention, in each of which diagrams the rotor is at astandstill with the border between an S pole and an N pole of the magnetof the rotor coincident with the center of the field coil Lv of thestator;

[0013]FIGS. 2a and 2 b are schematic diagrams illustrating the principleof a rotor position detecting method according to one embodiment of thepresent invention, in each of which diagrams the rotor is at astandstill with the border between an S pole and an N pole of the magnetof the rotor shifted a little from the center of the field coil Lv tothe field coil Lw of the stator.

[0014]FIGS. 3a and 3 b are schematic diagrams illustrating the principleof a rotor position detecting method according to one embodiment of thepresent invention, in each of which diagrams the rotor is at astandstill with the border between an S pole and an N pole of the magnetof the rotor shifted a little from the center of the field coil Lv tothe field coil Lu of the stator;

[0015]FIGS. 4a and 4 b are graphs showing the relation between theposition of the rotor relative to the stator and induced voltages at thenon-conducting phases, obtained by an experiment conducted by thepresent inventors;

[0016]FIG. 5 is a waveform diagram with respect to a three-phase motor,showing a relation between detection results on the positive andnegative polarities of induced voltages Eu, Ev and Ew detected at thefield coils Lu, Lv and Lw and leakage fluxes to the non-conductingphases, and showing a relation between leakage fluxes to thenon-conducting phases and torques (back electromotive forces) of therespective field coils Lu, Lv and Lw when the motor is rotating;

[0017]FIG. 6 is a block diagram of brushless motor drive controlapparatus according to one embodiment of the present invention in amotor driver unit used in a hard disk storage device;

[0018]FIG. 7 is a block diagram of a brushless motor drive controlapparatus according to one embodiment of the present invention in amotor driver unit used in a hard disk storage device;

[0019]FIG. 8 is a flowchart showing the operation procedure of theapparatus in FIG. 7;

[0020]FIG. 9 is a timing chart showing the operation of the apparatus inFIG. 7 determining the rotor position by conducting a pulse currentthrough the field coils of respective phases and detecting inducedvoltages at the non-conducting phases according to the procedure shownin FIG. 8;

[0021]FIG. 10 is a block diagram for explaining the motor driver unit,which is used in a hard disk storage device and which includes thebrushless motor drive control apparatus according to one embodiment ofthe present invention;

[0022]FIG. 11 is a flowchart showing a control procedure from startingthe motor till a constant speed operation in a motor driver unitincluding the brushless motor drive control apparatus according to oneembodiment of the present invention; and

[0023]FIG. 12 is a block diagram showing a representative configurationof the hard disk device as an example of a system using the motor driverunit including the brushless motor drive control apparatus according toone embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

[0024] Embodiments will be described with reference to the accompanyingdrawings.

[0025] Before proceeding with the description of the embodiments of thepresent invention, explanation will be made of the principle of rotorposition detection, on which those embodiments are based, by referringto FIGS. 1a, 1 b, 2 a, 2 b, 3 a and 3 b. These figures schematicallyillustrate the relation of any three field coils Lu, Lv and Lwrepresenting 3×n (n is a positive integer) coils with respect to therotor magnet in order to explain the positional relation of the fieldcoils of the stator with respect to the rotor magnet MG in a three-phasetype polyphase brushless motor. The PIO denotes a phase current outputcircuit to pass currents through the field coils Lu, Lv and Lw. Thisphase current output circuit outputs a total of six currents (includingcurrents in mutually opposite directions) to conduct them through anypair of field coils according to a specified sequence to thereby rotatethe rotor. In FIGS. 1a, 1 b, 2 a, 2 b, 3 a and 3 b, the rotor magnet MGand the stator field coils Lu, Lv and Lw are arranged linearly but theyare arranged coaxially in a real motor.

[0026]FIG. 1a shows that the rotor is at a standstill with the borderbetween an S pole and an N pole of the magnet MG of the rotor coincidentwith the center of the field coil Lv of the stator. Under thiscondition, when a short pulse current Iw is supplied from a phasecurrent output terminal W, to which the field coil Lw is connected, to aphase current output terminal U, to which the field coil Lu isconnected, the magnetic lines DMu produced by the field coil Lu arealmost in the same direction as the magnetic lines DMr1 from the N poleof the magnet MG of the rotor facing the field coil Lu and, moreover,the magnetic lines DMw produced by the field coil Lw are almost in thesame direction as the magnetic lines DMr2 of the S pole of the magnet MGof the rotor facing the field coil Lw. However, the magnetic lines DMuof the field coil Lu is in a direction opposite to the direction of themagnetic lines DMw of the field coil Lw. Because the border between theS pole and the N pole of the magnet MG coincides with the center of thefield coil Lv of the stator, the leakage flux from the field coil Lu tothe field coil Lv is the same in magnitude with and opposite indirection from the leakage flux from the field coil Lw to the field coilLv and therefore they cancel each other, so that the induced voltage inthe field coil Lv is zero.

[0027] Under this condition, to pass a current through the field coilsLu and Lw in reverse direction, a short pulse current Iu is suppliedfrom the phase current output terminal U to the phase current outputterminal W as shown in FIG. 1b, the magnetic lines produced by the fieldcoils Lu and Lw are respectively opposite in direction to the magneticlines emerging from the N poles and going into the S poles of the magnetMG of the rotor which respectively face the field coils Lu and Lw.Therefore, the flux densities in the field coils Lu and Lw are lowerthan in FIG. 1a, and the leakage fluxes from the field coils Lu and Lwto the field coil Lv are small but are the same in magnitude andopposite in direction as in FIG. 1a, so that they cancel each other andthe induced voltage in the field coil Lv is zero.

[0028] Description will now be made of the state that the rotor is at astandstill with the border of an S pole and an N pole of the magnet MGof the rotor being located a little shifted from the center of the fieldcoil Lv to the field coil Lw as in FIG. 2a. Under this condition,because the N pole of the magnet MG squarely faces the front side of thefield coil Lu, the density of the flux emerging from that portion of themagnet MG of the rotor which faces the field coil Lu and then passingthrough the field coil Lu is higher than the density of the fluxemerging from that portion of the rotor magnet MG which faces the fieldcoil Lw and then passing through the field coil Lw. Therefore, if ashort pulse current Iu is supplied from the phase current outputterminal W to the phase current output terminal U, the magnetic linesDMu produced by the field coil Lu is in the same direction as theabove-mentioned flux (magnetic lines) emerging from that portion of therotor magnet MG which faces the field coil Lu and then passing throughthe field coil Lu, and the magnetic lines DMw produced by the field coilLw is also in the same direction as the above-mentioned flux (magneticlines) emerging from that portion of the rotor magnet MG which faces thefield coil Lw and then passing through the field coil Lw. However, dueto the above-mentioned difference in flux density, the leakage flux ML1from the field coil Lu to the field coil Lv is larger than the leakageflux ML2 from the field coil Lw to the field coil Lv, so that a voltageis induced in the field coil according to the difference in leakageflux.

[0029] On the other hand, as in FIG. 2a, under the condition that therotor is at a standstill with the border between an S pole and an N poleof the rotor magnet MG being shifted a little from the center of thefield coil Lv to the field coil Lw of the stator, the direction in whichthe current is supplied is reversed, and a short pulse current Iu isconducted from the phase current output terminal U to the phase currentoutput terminal W as shown in FIG. 2b. Though the density of the fluxemerging from the rotor magnet MG and then passing through the fieldcoil Lu and the density of the flux emerging from the rotor magnet MGand then passing through the field coil Lw are the same as in FIG. 2a,the directions of the magnetic lines produced by the field coils Lu andLw are opposite to the directions of the magnetic lines emerging fromthe N poles and going into the S poles of the magnet MG of the rotorthat respectively face the field coils. In addition, the magnetic linesof the field coil Lu are set off by the N pole of the rotor magnet MG toa greater extent than the magnetic lines of the field coil Lw are setoff by the S pole. Therefore, the leakage flux ML1 from the field coilLu to the field coil Lv is smaller than the leakage flux ML2 from thefield coil Lw to the field coil Lv, but because the directions of theleakage fluxes ML1 and LM2 are reverse from those in FIG. 2a, thepolarity of the voltage induced in the Lv by the difference in leakageflux is the same as in FIG. 2a.

[0030] Moreover, in the above case, the voltage induced in the fieldcoil Lv is greater when a current is sent such that the magnetic linesproduced by the field coils Lu and Lv are in the same direction as themagnetic lines of the rotor magnet MG as in FIG. 2a than when a currentis sent such that the magnetic lines produced by the field coils Lu andLv are in the opposite direction to the direction of the magnetic linesof the rotor magnet MG. Therefore, by passing a current through thefield coils Lu and Lw alternately in opposite directions, detecting andcomparing the voltage induced in the field coil Lv, it is possible todetermine which poles are close to which field coils and whether thepoles are north or south.

[0031]FIG. 3a shows the state that the rotor is at a standstill with theborder between an S pole and an N pole of the magnet MG of the rotorbeing shifted a little away from the center of the field coil Lv of thestator to the field coil Lu. Under this condition, because the S pole ofthe rotor magnet MG squarely faces the front side of the field coil Lw,the density of the flux emerging from that portion of the rotor magnetMG which faces the field coil Lw and then passing through the field coilLw is higher than the density of the flux emerging from that portion ofthe rotor magnet MG which faces the field coil Lu and passing throughthe field coil Lu. Therefore, when a short pulse current Iw is suppliedfrom the phase current output terminal W to the phase current outputterminal U, the magnetic lines DMw produced by field coil Lw are in thesame direction as the above-mentioned flux (magnetic lines) emergingfrom that portion of the rotor magnet MG which faces the field coil Lwand passing through the field coil Lw and also the magnetic lines DMuproduced by the field coil Lu are in the same direction as theabove-mentioned flux (magnetic lines) emerging from that portion of therotor magnet MG which faces the field coil Lu and passing through thefield coil Lu. However, owing to the above-mentioned difference in fluxdensity, the leakage flux ML2 from the field coil Lw to the field coilLv is larger than the flux ML1 from the field coil Lu to the field coilLv and the voltage is induced in the field coil Lv according to thedifference in leakage flux. The voltage induced in the field coil Lv inFIG. 3a is opposite in polarity to the voltage induced in the field coilLv in FIGS. 2a and 2 b.

[0032] When the direction of current flow is reversed and a short pulsecurrent is conducted from the phase current output terminal U to thephase current output terminal W as shown in FIG. 3b, the density of theflux emerging from the rotor magnet MG and passing through the fieldcoil Lw is the same as the density of the flux emerging from the rotormagnet MG and passing through the field coil Lu as in FIG. 3a, but themagnetic lines produced by the field coils Lw and Lu are respectivelyopposite in direction to the magnetic lines from the S and the N polesof the rotor magnet MG facing those field coils. Moreover, the magneticlines produced by the field coil Lw are set off by the S pole of therotor magnet MG to a greater extent than the magnetic lines produced bythe field coil Lu are set off by the N pole of the rotor magnet MG.Therefore, though the leakage flux ML2 from the field coil Lw to thefield coil Lv is smaller than the leakage flux ML1 from the field coilLu to the field coil Lv, because the direction of the magnetic lines ML1and ML2 is opposite to that in FIG. 3a, the polarity of the voltageinduced in the field coil Lv according to the difference in leakage fluxis the same as in FIG. 3a.

[0033] In addition, the voltage induced in the field coil Lv is largerwhen a current is supplied such that the magnetic lines produced are inthe same direction as the magnetic lines of the rotor magnet MG as shownin FIG. 3a as in FIGS. 2a and 2 b than when a current is supplied suchthat the magnetic lines produced by the field coils Lu and Lv arerespectively opposite in direction to the magnetic lines of the rotormagnet MG as shown in FIG. 3b. Therefore, also in this case, by passinga current through the field coils Lu and Lw alternately in oppositedirections, detecting and comparing the voltage induced in the fieldcoil Lv, it is possible to determine which poles are close to whichfield coils and whether the poles are north or south. Note that thepolarity of the greater one of the leakage fluxes detected is oppositeto that detected in the case of FIG. 2.

[0034]FIG. 4a shows a result of a test conducted by the inventors. Thevertical axis indicates the detected values of the induced voltage andthe horizontal axis indicates the position of the rotor with respect tothe stator expressed in electrical angles. For example, in a motor witha 12-pole rotor, a mechanical angle of 60 degrees corresponds to anelectrical angle of 360 degrees. In other words, FIG. 4a shows theresult of measurement of voltages induced in the field coil Lv bypassing a current through the field coils Lu and Lw alternately inopposite directions.

[0035] In FIG. 4a, the solid line A indicates the induced voltage in thefield coil Lv when a current is conducted from the field coil Lw to thefield coil Lu and the broken line B indicates the induced voltage in thefield coil Lv when a current is conducted from the field coil Lu to thefield coil Lw. From FIG. 4a, one of the zero-cross points of the twocurves (A and B) is not clear, in other words, it is difficult touniquely determine the positional relation between the rotor and thestator from induced voltages detected when a current was sent in onedirection. Therefore, if an attempt is made to determine the rotorposition from induced voltages by a current supplied in one direction,errors are likely to occur. So, the inventors combined (add up) theabove two curves by way of trial, and found as indicated by the brokenline C in FIG. 4b that the zero-cross points became clear and the rotorposition can be determined with high accuracy.

[0036] According to an aspect of the present invention, the presentinvention is based on an idea of providing the brushless motor drivecircuit with a circuit for determining a pair of phases at which currentconduction is started by conducting a pulse current through two fieldcoils alternately in opposite directions, combining (adding) thevoltages induced in the non-conducting-phase field coil by respectivecurrents and sampled and held by a sample-and-hold circuit, orintegrating and then adding up the respective induced voltages, and onthe basis of the sum, detecting the polarities of the induced voltages.

[0037]FIG. 5 shows with regard to a three-phase motor the relationbetween detected polarities (positive and negative) of the inducedvoltages Eu, Ev and Ew detected at the field coils Lu, Lv and Lw and theleakage fluxes φu, φv and φw to the non-conducting-phase field coils,and the relation between the leakage fluxes φu, φv and φw to thenon-conducting-phase field coils and the torque Tu, Tv and Tw, namely,the back electromotive forces of the field coils Lu, Lv and Lw while themotor was at a standstill.

[0038] If the polarity-detecting results for the detected inducedvoltages Eu, Ev and Ew when the motor is at a standstill are “+, +, −”for example, by conducting a current from the u-phase field coil Lu tothe v-phase field coil Lv to start the motor, the maximum torque can beobtained. It is understood from FIG. 5 that the positions where thepolarities of the induced voltages are inverted coincide with thepositions where the polarities of the leakage fluxes are inverted and itnever occurs that detection about the polarity of induced voltages isunclear. Moreover, because the leakage flux is proportional to the fluxdensity in the field coil, it is not always required to make magneticsaturation occur in the field coil when detecting an induced voltage.Therefore, it is possible to make this determination by passing asmaller pulse current as compared with one of the conventional controlmethods in which a determination is made on a pair of phases at which tostart current conduction by detecting the rotor position based ondifferences in current rise time constant.

[0039] Table 1 shows the relation between the polarity detection resultsfor the combined induced voltages Eu, Ev and Ew and the phases forstarting current conduction. Obviously, the relation in Table 1corresponds to the relation shown in FIG. 5. After the polaritydetection result is obtained, by arranging for a determination to bemade on a pair of phases at which to start current conduction withreference to Table 1, the motor can be started in the correct rotatingdirection in a shortest time regardless of the rotor position at themoment. The polarity (positive or negative) detection results of theinduced voltages Eu, Ev and Ew can never be all “+” or all “−” wheninduced voltages are detected normally at the field coils of therespective phases. Therefore, if such detection results are given, thisshould be regarded as caused by detection errors and detection should becarried out over again. TABLE 1 START CURRENT CONDUCTION PHASES INDUCEDVOLTAGE (DIRECTION OF EU Ev EW CURRENT FLOW) DETECTION negative negativepositive phase v → phase u RESULT positive negative positive phase w →phase u positive negative negative phase w → phase v positive positivenegative phase u → phase v negative positive negative phase u → phase wnegative positive positive phase v → phase w

[0040] Meanwhile, in a real motor, even if the rotor and the stator arein the positional relation shown in FIGS. 1a and 1 b, in other words,even if the center of the field coil Lv coincides with the borderbetween an S pole and an N pole of the rotor, when a current is passedthrough the field coils Lu and Lw, the leakage flux from either one ofthose field coils to the field coil Lv is greater than the leakage fluxfrom the other coil due to, for example, variation in winding of thecoils, and a voltage proportional to a difference in leakage flux isinduced in the field coil Lv. However, in FIG. 1a, a current is suppliedsuch that the magnetic lines of the field coils are in the samedirection as the magnetic lines of the rotor magnet, whereas, in FIG.1b, a current is supplies such that the magnetic lines of the fieldcoils are in the opposite direction to the magnetic lines of the rotormagnet. Therefore, in these two cases, the voltages induced in the fieldcoil Lv ascribable to variation in winding are mutually opposite inpolarity, and when these induced voltages are added together, theycancel each other and become zero.

[0041]FIG. 6 shows a brushless motor drive control apparatus mounted ina motor driver unit for use in a hard disk device and structuredaccording to one embodiment of the present invention.

[0042] In FIG. 6, reference numeral 11 denotes a phase current outputcircuit that supplies current to the field coils Lu, Lv and Lw in athree-phase brushless motor, 12 denotes a phase switching controlcircuit that supplies a selection signal of the phases, through which acurrent is to be passed, to the phase current output circuit 11, 13denotes an induced voltage detecting circuit, connected to the outputterminals U, V and W of the phase current output circuit 11, fordetecting induced voltages, 14 a and 14 b denote sample-and-holdcircuits for sampling and holding the induced voltages detected by theinduced voltage output circuit 13 when the field coils are supplied witha current in two opposite directions, and 15 denotes an adder circuitthat adds up the voltages held in the sample-and-hold circuits 14 a and14 b and generates a rotor position signal.

[0043] Reference numeral 16 denotes a polarity detecting circuit fordetecting the polarity of an addition result in the adder circuit 15, inother words, detecting whether the sum of voltages is positive ornegative, and generating a polarity signal, 17 a, 17 b and 17 c denotedata latch circuits for storing polarity data representing polaritysignals generated by the polarity detecting circuit 16 when a current ispassed through the field coils, 18 denotes a discriminating circuit fordetermining rotor position, in other words, a pair of phases throughwhich a current is to be supplied in the first place based on polaritydata stored in the data latch circuits 17 a, 17 b and 17 c, from therelation in Table 1, for example, and generating a phase selectionsetting signal, 19 denotes a timing circuit that generates controlsignals based on a clock signal CLK, and outputs to the circuit blocks11 to 18.

[0044] The timing circuit 19 supplies a phase selection switching timingsignal T.CLK and a rotor position detection ON/OFF signal STR to thephase switching control circuit 12, an ON/OFF signal SNS to the inducedvoltage detecting circuit 13, a sampling timing signal SPR to thesample-and-hold circuits 14 a and 14 b, an operation timing signal ADDand a reset signal RST to the adder circuit 15, latch timing signals LTAto LTC to the data latch circuits 17 a, 17 b and 17 c, a determininationtiming signal JDG to the discriminating circuit 18. The circuit blocks11 to 18 operate sequentially by control signals from the timing circuit19.

[0045] By provision of this timing circuit 19, it becomes possible torealize a drive control apparatus which can start a brushless motor in ashort time by determining by itself a pair of phases at which to startcurrent conduction when a clock signal is only given without controlsignals being generated and supplied externally.

[0046] When the ON/OFF signal STR issued from the timing circuit 19 isat its effective level, the phase switching control circuit 12 sends aphase selection control signal to the phase current output circuit 11 todetect the rotor position and pass a small-pulse current through thefield coils. In response to the phase selection control signal from thephase-switching control circuit 12, the phase current output circuit 11sends a pulse current, having such a short duration as the rotor doesnot react, to any pair of field coils Lu, Lv and Lw in one direction orin the opposite direction. On the other hand, when the phase switchingcontrol circuit 12 receives a phase selection setting signal COMMSTindicating the phases at which to start current conduction, from thediscriminating circuit 18, the phase switching control circuit 12 sendsa phase selection control signal to the phase current output circuit 11directing it to pass a pulse current through the set phases at which tostart current conduction to rotate the motor. At this time, the ON/OFFsignal STR from the timing circuit 19 is at the effective level.

[0047] The induced voltage detecting circuit 13 has a rotor positiondetecting action ON/OFF signal SNS supplied from the timing circuit 19and also has another signal, indicating which phases are being selected,supplied from the phase switching control circuit 12. By those signals,the induced voltage detecting circuit 13 detects and amplifies thevoltage induced in the non-conducting-phase coil. The induced voltagedetecting circuit 13, if formed by a MOSFET, may include a switch(selector) to select a voltage of the non-conducting phase, wherecurrent is not flowing, out of the output terminals U, V and W of thephase current output circuit 11 and also an amplifier circuit to amplifythe selected voltage. If formed by a bipolar transistor, the inducedvoltage detecting circuit 13 may include three differential amplifiersthat each have at one input terminal supplied with one of the voltagesof the output terminals U, V and W of the phase current output circuit11 and at the other input terminal supplied with the potential at thecommon connection node N0 of the respective field coils. When theinduced voltage detecting circuit 13 is formed by three differentialamplifier circuits, the circuit 13 may be configured such that any oneof the differential amplifier circuits performs amplification when itscurrent source is turned on by a phase selection control signal.

[0048] The adder circuit 15 may be an analog adder circuit using anoperational amplifier or may be a digital adder circuit. In the case ofa digital adder, it is only necessary to insert an A/D converter circuitas the stage subsequent to the sample-and-hold circuits 14 a and 14 b.The polarity detecting circuit 16 may be an analog or digital circuitdepending on the type of the adder circuit 15. If the adder 15 is formedas a digital circuit, the polarity detecting circuit 16 may be formed bya subtractor. In place of the sample-and-hold circuits 14 a and 14 b,registers may be used, and an A/D converter circuit may be provided atthe preceding stage to have the detected induced voltage converted intoa digital value and stored as digital data in the registers.

[0049] In the above embodiment, the discriminating circuit 18 thatdesignates start current conduction phases from a polarity detectionresult is mounted together with the induced voltage detecting circuit13, etc. However, it is possible to provide a microcomputer thatreceives polarity data from the latch circuits 17 a to 17 c, which holddata from the polarity detecting circuit 16, and determines a pair ofphases at which to start current conduction and sets the phase data inthe phase switching control circuit 12.

[0050]FIG. 7 shows a motor drive control apparatus in a motor driverunit, which is used in a hard disk storage device and which isstructured according to another embodiment of the present invention.

[0051] This embodiment uses an integrating circuit 20, which hasreplaced the sample-and-hold circuits 14 a and 14 b and the adder 15 inthe embodiment shown in FIG. 6. This integrating circuit 20 may beformed by a well-known integrating circuit including a CR integratingcircuit made of a capacitor and a resistance, or by a well-knownintegrating circuit including an operational amplifier and a capacitorconnected between an output terminal and an inverted input terminal ofthe amplifier.

[0052] In this embodiment, by a control signal from the timing circuit19, the integrating circuit integrates an induced voltage which isdetected at the non-conducting phase by the induced voltage detectingcircuit 13 when a pulse current is passed through the field coils in onedirection in the first place and, under the condition that the result ofintegration is maintained, also integrates an induced voltage which isdetected at the non-conducting phase by the induced voltage detectingcircuit 13 when a pulse current is passed through the field coils in theopposite direction. The polarity detecting circuit 16 is used to detectthe polarity of the electric charge remaining in the capacitor as acomponent part of the integrating circuit (hereafter referred to as anintegrating capacitor). After this determination is made, control isperformed so that the integrating capacitor is reset once, and then apulse current is passed through a subsequent pair of field coils, andthe induced voltage detected is integrated.

[0053] Description will be made of the operation of the motor drivecontrol apparatus in FIG. 7 with reference to a flowchart in FIG. 8.FIG. 8 shows the operation procedures of the phase current outputcircuit 11 at left and the induced current detecting circuit 13 and theintegrating circuit 20 at right to show the related actions comparedwith each other.

[0054] When the enable signal EN (Refer to FIGS. 9 and 10) from acontrol circuit is asserted to the low level, the timing circuit 19starts to generate a control signal for detecting the rotor position.With this action got started, in the first step S0, while the outputterminals of the phase current output circuit 11 are in high impedancestate in which the terminals are all opened, that is, no current isoutput from any phase output terminal, the capacitor of the integratingcircuit 20 is reset, more simply, the capacitor discharges itself ofelectric charge. Next, a pulse current is passed from the phase v to thephase w by the phase current output circuit 11. The pulse current usedhas so short a duration as the rotor does not react to it. The inducedvoltage of the phase u, which is non-conducting at this moment, isdetected by the detecting circuit 13, and is integrated by theintegrating circuit 20 (Step S1).

[0055] Subsequently, in a step S2, all phase terminals of the phasecurrent output circuit 11 are opened, and for this while the voltageintegrated in the integrating circuit 20 is held. In the next step S3,the phase current output circuit 11 sends a pulse current from the phasew to the phase v in the opposite direction to the current flow in thestep S1. At this time, the induced voltage of the phase u in thenon-conducting state is detected by the induced voltage detectingcircuit 13, and the phase-u induced voltage is integrated using theresult of the previous integration as the initial value. Accordingly, inthe integrating capacitor, the integration result of the phase-u inducedvoltage when a current was passed from the phase v to the phase w isadded with the integration result of the phase-u induced voltage when acurrent was passed from the phase w to the phase v.

[0056] In the step S4, the polarity of the electric charge remaining inthe integrating capacitor is detected by the polarity detecting circuit16, and a detection decision result u-DATA is stored in the firstcircuit 17 a. All the output terminals of the phase current outputcircuit 11 are opened, and in the integrating circuit 20, the electriccharge held in the integrating capacitor is reset. In a step S5, thephase current output circuit 11 passes a pulse current from the phase wto the phase u. At this time, the induced voltage of the phase v, whichis not conducting, is detected by the detecting circuit 13, and theinduced voltage is integrated by the integrating circuit 20.

[0057] In a step S6, the voltage integrated by the integrating circuit20 is held, and all output terminals of the phase current output circuit11 are opened. In the next step S7, the phase current output circuit 11passes a pulse current from the phase u to the w phase in the directionopposite from the the direction in the step S5, the induced voltage ofthe phase v, which is not conducting, is detected by the detectingcircuit 13, and the integrating circuit 20 integrates the phase-vinduced voltage using the previous integration result as the initialvalue.

[0058] Subsequently, in a step S8, after twice integration, the polarityof the charge remaining in the integrating capacitor is detected by thepolarity detecting circuit 16. The detection result v-DATA in the seconddata latch circuit 17 b. In addition, all phase terminals of the phasecurrent output circuit 11 are opened, and the charge held in theintegrating capacitor in the integrating circuit 20 is reset.

[0059] In steps S9 to S11, as in the above-mentioned steps S5 to S7, thephase current output circuit 11 passes a pulse current from the phase uto the phase v, the induced voltage of the phase w, which is notconducting, is detected by the detecting circuit 13, and is integratedby the integrating circuit 20. Subsequently, a reverse pulse current ispassed from the phase u to the phase v, the induced voltage of the phasew, which is not conducting, is detected by the detecting circuit 13, andthe phase-w induced voltage is integrated by the integrating circuit 20.

[0060] In the next step S12, from results of twice integration in theintegrating circuit 20, the polarity of the charge remaining in theintegrating capacitor is detected by the polarity detecting circuit 16,and a detection result w-DATA is stored in the third data latch circuit17 c. All phase output terminals of the phase current output circuit 11are opened, and the charge held in the integrating capacitor is reset inthe integrating circuit 20.

[0061] After this, in a step S13, the discriminating circuit 18determines the position of the rotor based on detection results u-DATA,v-DATA and w-DATA stored in the data latch circuits 17 a, 17 b and 17 cin the steps S3, S7 and S11. More specifically, the discriminatingcircuit 18 determines the rotor position according to Table 1 from threepieces of information indicating the positive or negative polaritystored in the data latch circuits 17 a, 17 b and 17 c, and, from therotor position, determines the phases at which current conduction isstarted, and sends a phase selection setting signal COMMST to the phaseswitching control circuit 12 to initialize the current conductionphases.

[0062] In determining the rotor position in the step S13, it isimprobable that the polarity detection results (positive or negative)stored in the data latch circuits 17 a, 17 b and 17 c are all “+” (H) orall “−” (L) and, therefore, if such a combination of results occurs,they should be regarded as detection errors, and the process shown inFIG. 8 returns to the step S0 to perform rotor position detection. In amotor drive control apparatus in the embodiment shown in FIG. 7, whenthe apparatus is operated in synchronism with a clock signal CLK with afrequency of 3.5 kHz, for example, the steps S0 to S13 can be finishedin a time as short as 2 msec. Therefore, even if the rotor positiondetection is carried out over again, this has hardly any effects on thestarting time of the motor that takes several tens of msec.

[0063]FIG. 9 is a timing chart when the rotor position is detected bysupplying a pulse current to the respective phases sequentially anddetecting the induced voltages at the non-conducting phases according tothe above-mentioned procedure. In FIG. 9, u, v and w denote the outputvoltages of the phases of the phase current output circuits 11, Iu, Ivand Iw denote the currents that flow in the field coils Lu, Lv and Lw,SNS denotes an ON/OFF control signal for integrating actions to theintegrating circuit 20, RST denotes a reset signal to discharge thecharge of the integrating capacitor, LTA, LTB and LTC denote signals forgiving latch timing to the data latch circuits 17 a, 17 b and 17 c, JDGdenotes a signal for giving discrimination timing to the discriminatingcircuit 18, and COMMST denotes a timing signal which the discriminatingcircuit 18 issues to initialize the phase selection in the phaseswitching control circuit 12 based on a discrimination result. Clockcycles T0 to T13 in FIG. 9 respectively correspond to steps S0 to S13 inthe flowchart in FIG. 8.

[0064]FIG. 10 shows an example of system configuration including a motordriver unit, which includes a motor drive control apparatus according toanother embodiment of the present invention, and which is used in a harddisk storage device. The circuit blocks and circuit elements located ina range enclosed by a broken line 210 in FIG. 10 are formed on onesemiconductor substrate, such as a single crystal silicon chip, but theyare not to be construed as restrictive.

[0065] In FIG. 10, the circuits designated by the same referencenumerals as in FIG. 7 are the circuits, which have or include the samefunctions. Specifically, reference numeral 11 denotes a phase currentoutput circuit that selectively and sequentially supplies current to thethree-phase field coils Lu, Lv and Lw of a spindle motor to rotate thedisks of a hard disk device, 12 denotes a phase switching controlcircuit to supply to the phase current output circuit 11 a signal forselection of the phases through which to pass a current (phase selectioncontrol signal), 19 denotes a timing circuit to generate control signalsto the above-mentioned circuit blocks 11 through 18 based on a clocksignal CLK.

[0066] In this embodiment, out of the circuit blocks shown in FIG. 7 (orFIG. 6), the induced voltage detecting circuit 13, connected to theoutput terminals U, V and W of the phase current output circuit 11, fordetecting the induced voltages, the integrating circuit 20 (orsample-and-hold circuits 14 a and 14 b, and an adder 15) for integratinginduced voltages detected by the induced voltage detecting circuit 13,the polarity detecting circuit 16 for detecting the polarity ofintegration results (or addition results), the data latch circuits 17 a,17 b and 17 c for storing polarity detection results, and thediscriminating circuit 18 for discriminating the rotor position, thatis, a pair of phases through which a current is conducted in the firstplace from detection results stored in the data latch circuits 17 a, 17b and 17 c are collectively shown as a single start current conductionphase determining circuit 21.

[0067] In this embodiment, the start current conduction phasedetermining circuit 21 is connected to external terminals P1 and P2 onthe chip, and the terminals P1 and P2 are connected to anexternally-mounted discrete capacitor C1 as the integrating capacitor ofthe integrating circuit. This integrating capacitor serves to eliminatenoise in detected voltages in the induced voltage detecting circuit 13that detects the induced voltages at the non-conducting phases todetermine start current conduction phases with high accuracy. Thisembodiment is particularly effective in a case where the phase currentoutput circuit 11 is formed by a bipolar transistor. This is becauselarge noise is contained in the induced voltages at the non-conductingphases when the phase current output circuit 11 is a bipolar transistortype than when it is a MOSFET type.

[0068] In FIG. 10, 23 denotes a back e.m.f. detecting circuit thatmonitors the voltages at the output terminals U, V and W of the phasecurrent output circuit 11 when they are non-conducting, detectszero-cross points of the back e.m.f., and gives a phase switching timingsignal to the phase switching control circuit 12, 22 denotes a PLL(phase locked loop) circuit including a voltage-controlled oscillator(VCO) that generates an oscillating signal required to give phaseswitching timing to the phase switching control circuit 12 duringconstant-speed rotation based on an output signal of the back e.m.f.detecting circuit 23, 24 denotes a brake control circuit for forciblyapplying an induction brake by shorting all field coils by turning offthe power supply switch Qsw of the phase current output circuit 11 whenbringing the motor to a stop, and 25 denotes a speed control circuit forcontrolling the motor speed by detecting the current flowing in thephase current output circuit 11, and, in response to a speed-relatedcommand signal SPNCTL from a microcomputer, increasing the rotationspeed by increasing the current applied to the phase current outputcircuit 11 or reducing the speed by decreasing the applied current.

[0069] The PLL circuit 22 is connected to external terminals P3, P4 andP5 provided on the chip, and the external terminals P3, P4 and P5 areconnected with externally-mounted elements, such as capacitors C0 and C1and a resistance R1, which form a loop filter of the PLL, and acapacitor C2 and a resistance R2, which determine an oscillationfrequency of the VCO. The parts mounted on the motor driver IC chip 210include a protecting circuit 26 for detecting the temperature of thechip and bringing the operation of the circuit to a stop, a boostingcircuit 27 for boosting the gate voltage to make it possible tosufficiently drive MOSFET's used, a voltage regulator 28 to supply apower source voltage to the IC or LSI provided around the motor driverIC chip 210, and a VCM drive control circuit 30 for driving the voicecoil motor to move the magnetic heads, but they should not be construedas restrictive.

[0070] The VCM drive control circuit 30 comprises a VCM driving circuit31 for outputting current to drive the driving coil L VCM of the voicecoil motor, a serial port 32 for serial transmission and reception toand from the microcomputer, a D/A converter circuit 33 for convertingcontrol data received from the microcomputer into an analog signal andsupplying to the VCM driving circuit 31, a back e.m.f. detecting circuit34 for detecting the back e.m.f. of the coil L VCM to obtain speedinformation when starting the motor, an A/D converter circuit 35 forconverting a detected back e.m.f. into a digital signal, a power supplyvoltage monitoring circuit 36 for monitoring the levels of power supplyvoltages Vss and Vdd to detect power cut-off, and a head retractiondrive circuit 37 for controlled driving of the coil L VCM to enable themagnetic heads to retract to outside the disk surface when power cut-offis detected.

[0071] The above-mentioned serial port 32 sends and receives serial dataDATA based on a serial clock SCLK or a load instruction signal LOAD fromthe microcomputer and generates control signals, such as an enablesignal VCMEN to the VCM driving circuit 31 based on data received. Theserial port 32 also sends to the microcomputer an A-D converted versionof a back e.m.f. induced in the coil LVCM when the motor is started, theback e.m.f. being detected by the back e.m.f. detecting circuit 34 forobtaining speed information from the detected back e.m.f. Thus, themicrocomputer control the motor speed by monitoring motor speedinformation so that the magnetic head is prevented from falling on thehard disk surface faster than a specified speed.

[0072] Further, the serial port 32 has a function to generate an enableEN signal to the timing generating circuit 19 of the spindle motorcontrol system based on data received from the microcomputer, andgenerates control signals, such as a phase selection setting signalCOMM. Note that when the phase switching control circuit 12 starts themotor by a phase selection setting signal COMMST supplied from the startcurrent conduction phase determining circuit 21 as in theabove-mentioned embodiment, it becomes unnecessary to send a phaseselection setting signal COMM from the microcomputer. However, withoutmounting the discriminating circuit 18 for discriminating the startcurrent conduction phases from a polarity detection result in the startcurrent conduction phase determining circuit 21 and if it is arrangedthat the microcomputer receives information from the latch circuits 17 ato 17 c, which store polarity data, and determines and sets a pair ofphases for start current conduction in the phase switching controlcircuit 12, the above-mentioned route passing through the serial port 32can be used to initialize the phase switching control circuit 12.

[0073] Meanwhile, in the motor driver unit in this embodiment, there areprovided a power terminal P6 for a power source voltage Vss of 5V forexample, a power terminal P7 for a power supply voltage Vdd of 12V or5V, and a set of power terminals P8 for ground potential (0V). To thepower terminal P7, 12V is applied for use in a 3.5-inch hard diskdevice, or 5V is applied for use in a 2.5-inch hard disk device. P11 toP14 denote the terminals connected to the terminals of the field coilsof a spindle motor.

[0074]FIG. 11 shows a control procedure from starting of a motor till aconstant speed drive in the motor driver unit, which includes the startcurrent conduction phase determining circuit.

[0075] In this motor driver unit, when a start signal is given by themicrocomputer, the start current conduction phase determining circuit 21detects rotor position to begin with (step S21). This rotor positiondetection is performed by the steps S1 to S12 in the flowchart in FIG.8, which has been described. When the rotor position has been detected,a decision is made in a step S22 whether rotor data are all “L” (lowlevel) or all “H” (high level), if the decision result is “Yes”, whichmeans that data are all “L” or all “H”, rotor position determination(step S21) is performed again. It ought to be noted that the step S22corresponds to the S13 in FIG. 8. If the decision result is “No” in thestep S22, which means that position data are neither all “L” nor all“H”, the phases for start current conduction are set in the phaseswitching control circuit 12 by a signal COMMST based on detectionresults from the start current conduction phase determining circuit 21(step S23).

[0076] Subsequently, the phase switching control circuit 12 controls thephase current output circuit 11 to change over the coils that areexcited sequentially to conduct a drive current to the coils of themotor, to start synchronous driving (step S24). When the rotor starts torotate normally, back e.m.f develops in the non-conducting phases, and adecision is made in the next step S25 whether the back e.m.f. detectingcircuit 23 detected back e.m.f. If the back e.m.f. was not detected, adecision is made that the motor has not started, and the process returnsto the step 21 to perform rotor position detection again. On the otherhand, if back e.m.f. was detected, in a step S26, back e.m.f. driving isperformed which switches over the conducting phases according to timingof the zero-cross points detected by the back e.m.f. detecting circuit23 and the rotation is accelerated by an increase of current passedthrough the coils, and the motor enters constant-speed driving (stepS27).

[0077]FIG. 12 is a block diagram of an example of a hard disk device asa system including a motor driver unit according to one embodiment ofthe present invention.

[0078] In FIG. 12, reference numeral 100 denotes a recording medium suchas a magnetic disk, 110 denotes a spindle motor to drive the magneticdisk 100, 120 denotes a magnetic head including a write head and a readhead, and 130 denotes a voice coil motor to move the arm assembly withthe magnetic heads 120. Reference numeral 210 denotes a motor driverunit that can be realized by embodying the present invention, and themotor driver unit 210 drives both the spindle motor 110 and the voicecoil motor 130.

[0079] Reference numeral 220 denotes a read/write amplifier foramplifying a current, produced according to magnetic changes detected bythe magnetic head 120 to transmit a readout signal to a data channelprocessor 230, and for amplifying a write pulse signal from the datachannel processor 230 to supply a drive current to the magnetic head120. Reference numeral 240 denotes a hard disk controller for receivingreadout data RDT sent from the data channel processor 230, performing anerror correcting process thereon and performing an error correctioncoding process on write data from the host computer to supply theprocessed data to the data channel processor 230. The data channelprocessor 230 performs a modulation/demodulation process suitable fordigital magnetic recording and carries out a signal process, such aswaveform shaping or the like taking magnetic recording characteristicsinto account.

[0080] Reference numeral 250 denotes an interface controller thatcontrols exchange of data between this system and external equipment,and the hard disk controller 240 mentioned above is connected to a hostcomputer, such as the microcomputer of a personal computer, through theinterface controller 250. Reference numeral 260 denotes a microcomputerthat performs a comprehensive control of the whole system and calculatesa sector position from address information supplied from the hard diskcontroller 240, and 270 denotes a buffer cache memory for temporarilystoring read data read at high speed from the magnetic disk. Themicrocomputer 260 determines the operation mode from a signal sent bythe hard disk controller 240, and controls the related parts of thesystem according to the operation mode.

[0081] The motor driver unit 210, as described above, comprises aspindle motor drive part and a voice coil motor drive part. By a signalfrom the microcomputer 260, the spindle motor drive part isservo-controlled to make the relative speed of the heads constant andthe voice coil motor drive part is servo-controlled to make the centerof the head coincident with the center of a truck.

[0082] The hard disk control system 200 is formed by the motor driverunit 210, the read/write amplifier 220, the data channel processor 230,the hard disk controller 240, the interface controller 250, themicrocomputer 260, and the cache memory 270. The hard disk device isformed by the control system 200, the magnetic disks 100, the spindlemotor 110, the magnetic heads 120, and the voice coil motor 130.

[0083] Description has been made of the embodiments made by theinventors. However, the present invention is not limited to thoseembodiments, but obviously many changes and modifications of the presentinvention may be made without departing from the spirit or scope of theinvention. For example, in the above-mentioned embodiments, descriptionhas been made using a three-phase motor as an example, but the presentinvention is not limited to three-phase motors, but may be applied tothe driving circuits of two-phase motors and four-phase or otherpolyphase motors. Further, in those embodiments, the motor driver unitdescribed has been a composite type that includes not only the drivingcircuit of the spindle motor but also the driving circuit of the voicecoil motor mounted on one semiconductor chip. However, needless to say,the present invention may be applied to a semiconductor integratedcircuit having only the spindle motor driving circuit mounted on it.

[0084] Moreover, description has centered around the field as thebackdrop of the invention in which the invention made by the inventorsis applied to the motor driver unit of the hard disk storage device, butthe present invention is not limited to this area and may be utilized inmotor driver units for driving brushless motors, such as a motor todrive the polygon mirror of a laser beam printer or a motor for an axialflow fan.

[0085] According to the embodiments of the present invention, it ispossible to realize a semiconductor integrated circuit for brushlessmotor drive control and a brushless motor drive control apparatus, whichare capable of preventing a reverse rotation when starting the motor bydetecting the rotor position relative to the stator with less errors todetermine field coils at which current conduction is started.

What is claimed is:
 1. A brushless motor drive control apparatus for rotating a brushless motor by switching a current from one pair of field coils to another pair of field coils of a polyphase brushless motor having a plurality of field coils, comprising: a phase current output circuit for generating a current to pass through the field coils of respective phases of said motor; a phase switching control circuit capable of controlling said phase current output circuit to switch a current to pass from one pair of field coils to another pair of field coils of said motor to achieve constant-speed rotation and, when starting said motor, capable of controlling said phase current output circuit to conduct a pulse current, having such a duration as not to cause the rotor to react, to each of a plurality of field coil pairs of said motor alternately in first and second, mutually opposite, directions sequentially; an induced voltage detecting circuit, connected to said phase current output circuit, for detecting first and second voltages induced in field coils of a non-conducting phase by said pulse current in said first and second directions passed through each of said plurality of field coil pairs; a combining circuit for generating a rotor position signal by combining said first and second induced voltages detected by said induced voltage detecting circuit at each of the field coils of said non-conducting phase; a polarity detecting circuit for generating a polarity signal representing a polarity of a rotor position signal generated by said combining circuit at each of the field coils of said non-conducting phase; and a memory circuit for storing polarity data representing a plurality of polarity signal generated by said polarity detecting circuit, wherein a pair of field coils through which a current is to be conducted to start the motor is determined on the basis of multiple pieces of polarity data stored in said memory circuit, and wherein said phase switching control circuit is arranged to control said phase current output circuit to conduct a current through the field coil pair determined.
 2. A brushless motor drive control apparatus according to claim 1, further comprising a discriminating circuit for determining a field coil pair for current conduction to start said motor on the basis of multiple pieces of polarity data stored in said memory circuit and generating a phase selection setting signal to be supplied to said phase switching control circuit.
 3. A brushless motor drive control apparatus according to claim 2, wherein said combining circuit includes a sample-and-hold circuit for sampling and holding said first induced voltage and another sample-and-hold circuit for sampling and holding said second induced voltage, and an adder for adding together outputs of said first and second sample-and-hold circuits.
 4. A brushless motor drive control apparatus according to claim 2, further comprising a timing circuit for, on the basis of a clock signal, generating control signals to operate said phase switching control circuit, said induced voltage detecting circuit, said combining circuit, and said memory circuit at specified timing.
 5. A brushless motor drive control apparatus according to claim 2, further comprising a back e.m.f detecting circuit, connected to said phase current output circuit, for detecting zero cross points generated in the field coils of the non-conducting phase and generating a phase switching timing signal, wherein said phase switching control circuit switches a current from one field coil pair to another according to said phase switching timing signal from said back e.m.f. detecting circuit after the motor is started and said phase current output circuit supplies the motor with a current of a larger amplitude than that of said pulse current sent to determine a field coil pair for current conduction to start the motor.
 6. A brushless motor drive control apparatus according to claim 1, wherein said combining circuit includes a sample-and-hold circuit for sampling and holding said first induced voltage and another sample-and-hold circuit for sampling and holding said second induced voltage, and an adder for adding together outputs of said first and second sample-and-hold circuits.
 7. A brushless motor drive control apparatus according to claim 1, further comprising a timing circuit for, on the basis of a clock signal, generating control signals to operate said phase switching control circuit, said induced voltage detecting circuit, said combining circuit, and said memory circuit at specified timing.
 8. A brushless motor drive control apparatus according to claim 1, further comprising a back e.m.f detecting circuit, connected to said phase current output circuit, for detecting zero cross points generated in the field coils of the non-conducting phase and generating a phase switching timing signal, wherein said phase switching control circuit switches a current from one field coil pair to another according to said phase switching timing signal from said back e.m.f. detecting circuit after the motor is started and said phase current output circuit supplies the motor with a current of a larger amplitude than that of said pulse current sent to determine a field coil pair for current conduction to start the motor.
 9. A semiconductor integrated circuit for a drive control apparatus of a polyphase brushless motor having a plurality of field coils, comprising: a phase current output circuit for generating a current to pass through respective field coils of said motor; output terminals for outputting a current to pass through field coils of respective phases of said motor, said current being generated by said phase current output circuit; a phase switching control circuit capable of controlling said phase current output circuit to switch a current to pass from one pair of field coils to another pair of field coils of said motor for constant-speed rotation thereof and, when starting said motor, capable of controlling said phase current output circuit to conduct a pulse current, having such a duration as not to cause the rotor to react, to each of a plurality of field coil pairs of said motor alternately in first and second, mutually opposite, directions sequentially; an induced voltage detecting circuit, connected to said phase current output circuit, for detecting first and second voltages induced in each of said field coils of a non-conducting phase by said pulse current in said two directions; an integrating circuit for generating a rotor position signal by integrating said first induced voltage by said pulse current in said first direction and then integrating said second induced voltage by said pulse current in said second direction at each of said field coils of the non-conducting phase; a polarity detecting circuit for generating a polarity signal representing a polarity of a rotor position signal generated by said integrating circuit at each of said field coils of the non-conducting phase; a memory circuit for storing polarity data representing a plurality of polarity signal generated by said polarity detecting circuit; and a discriminating circuit for determining a field coil pair for current conduction to start said motor on the basis of multiple pieces of polarity data stored in said memory circuit and generating a phase selection setting signal to be supplied to said phase switching control circuit, each of said circuits and said output terminals being formed on a single semiconductor chip.
 10. A semiconductor integrated circuit according to claim 9, wherein said integrating circuit includes a capacitor element connected as an externally-mounted element to an external terminal provided on said semiconductor chip.
 11. A semiconductor integrated circuit according to claim 9, further comprising a timing circuit, mounted on said semiconductor chip, for generating control signals on the basis of a clock signal for operating said phase switching control circuit, said induced voltage detecting circuit, said integrating circuit, said memory circuit and said discriminating circuit respectively at predetermined timing.
 12. A semiconductor integrated circuit according to claim 9, further comprising a back e.m.f detecting circuit, mounted on said semiconductor chip and connected to said phase current output circuit, for detecting zero cross points generated in the field coils of the non-conducting phase and generating a phase switching timing signal, wherein said phase switching control circuit switches a current from one field coil pair to another according to said phase switching timing signal from said back e.m.f. detecting circuit after the motor is started and said phase current output circuit supplies the motor with a current of a larger amplitude than that of said pulse current sent to determine a field coil pair for current conduction to start the motor.
 13. A method for starting a polyphase brushless motor having a rotor containing a magnet and a stator containing a plurality of field coils, comprising the steps of: passing a pulse current, having such a duration as the rotor does not react, through each pair of field coils in first and second, mutually opposite, directions sequentially, each pair being formed by a field coil and one of the other field coils of said motor; generating first and second induced voltage signals by detecting voltages induced in each field coil of a non-conducting phase by a pulse current applied in said first and second directions; combining said first and second voltages at each field coil of the non-conducting phase to generate a plurality of rotor position signal representing the relative position of said rotor with respect to said stator; detecting polarities of said plurality of rotor position signal; and determining a field coil pair of the phases for current conduction to start said motor using detection results of polarities of said plurality of rotor position signal.
 14. A motor starting method according to claim 13, wherein said rotor position signal is generated by adding up said first and second induced voltage signals.
 15. A motor starting method according to claim 13, wherein said rotor position signal is generated by integrating said first induced voltage signal and, under the condition that the result of said integration is maintained, integrating second induced voltage signal. 